The present invention relates to an electromagnetic shielding screen for at least one electronic circuit disposed on a substrate, having side faces called vertical faces that form a band, and a face called upper face whose edges coincide with the upper edges of said vertical side faces, the band and the upper face being realized at least partly of an electrically conducting material and forming a sub-set provided for being applied against the supporting substrate of the circuit to be shielded.
Apparatus operating at high frequency, such as wireless telephones (called residentials), or mobile telephones (called cellulars), are to comprise shielding screens for components (electronic circuits) radiating at high frequency, so as to avoid the latter having disturbing electromagnetic influences. A known structure of such a shielding screen often consists of a band and a cap covering it, which together form a sub-set provided for being applied against the printed circuit board (or other support of the circuit to be shielded such as a ceramic substrate for a hybrid circuit, for example). This sub-set is realized at least partly with an electrically conducting material so as to realize a kind of Faraday cage for the protection of the circuit. Making the shielding in two separate parts permits to have access to the protected circuits, as required, notably for repair purposes, in which case the cap is opened.
The linking modes habitually found for fixing the cap onto the band are soldering, in which case the link is irreversible (or at least implies comparatively extensive practical manipulations), or solutions are used of the type in which strips or sliding members are used to form a spring and provide that the cap is locked to the band. This type of linking can easily be dismantled this time, but the attempts made show that shakes or shocks exerted on the structures thus realized often lead to the unwanted opening of the cap. Moreover, the fact that two parts are to be manufactured and then controlled as regards storage and positioning on the supporting substrate, brings with it extra cost compared with a shielding screen that would be formed by a single part, this aspect of the matter having much weight for consumer hardwarexe2x80x94as this is, in essence, the case herexe2x80x94of which the price is to be the lowest possible.
From Japan patent application JP-A-06 338695 is known an electromagnetic shielding screen whose upper surface is precut along a closed line of holes forming a dotted line, so as to be able to lift this upper surface when a component underneath it is to be replaced. However, a specific part must be provided for closing the screen again after repair, while this new part must permit to be clipped or soldered onto the remaining band, with the drawbacks cited and described above when the shielding screen consists of a band and a cap.
It is an object of the invention to realize an electromagnetic shielding screen that is made of a single part while permitting easy repair of the electronic components it protects.
It is another object of the invention to realize an electromagnetic shielding screen resistant to shocks and of low cost.
These objects are achieved and the prior-art drawbacks are mitigated thanks to the fact that the electromagnetic shielding screen indicated in the opening paragraph is characterized in that said band has a slightly pyramidical shape, while said side faces form an angle comprised between 92 degrees and 94 degrees relative to said upper face and in that said upper face has a precut running in parallel with and in proximity of its edges.
The shielding screen is preferably made of sheet steel and the precut of the upper face may be made either by a succession of holes lying close together, or, preferably, by partly cutting away the central part of the upper face, either operation being realized during the embossing of sheet steel that gives its shape to the screen. For repairing a circuit closed in by the screen, it is sufficient to lift the central precut part with any known means, to carry out the repair and then take a new screen that is identical with the original one and stamp it with force on that which remains of the original screen, that is to say, the side band, while the positioning by clamping is ensured by the steep slopes of the faces that form the band.